Studies On Polynuclear Complexes And Coordination Polymers Based On Amino Carboxylate Ligands

In recent years, a considerable interest has been focused on the novel coordination compounds because of their fascinating structural and topological features, and their potential application in functional materials and molecular recognition. Amino acids are polydentate organic ligands containing N, O atoms, which can coordinate to several metal ions and may exhibit various coordination modes. Thus they are good ligands for synthesizing novel complexes. We synthesized six new compounds by using amino acids as main ligands. The compounds have been characterized by IR, elemental analysis and single crystal X-ray diffraction. The thermogravimetric analysis (TGA) and magnetic properties of some complexes have been studied as well. The main work is listed below:1. A three-dimensional coordination polymer [Cu2(NH₂CH₂COO)-2(N₃)₂]_n (1) was prepared by using glycine and N₃^- as ligand and characterized by IR,elemental analysis and single crystal X-ray diffraction analysis. It was shown that complex (1) crystallized in the orthorhombic space group P2₁2₁2₁ with a = 7.160(2), b = 10.385(3), c = 11.173(3) A. The Cu(â…¡) ion is five-coordinated in a distorted square pyramid. N₃ˉadopts aμ1,1 (EO) bridging mode connecting Cu(II) ions into 1-D chains. In this complex, one glycine ion chelates to one Cu(II) ion using the amino group and one carboxylato oxygen atom. The remaining carboxylato oxygen atom coordinates to another Cu(II) ion. Therefore the 1D chains are further connected into a 3-D network structure by theμ₂-η3-O', O, N bridging glycinate. Magnetic investigation on complex (1) showed the existences of ferromagnetic interaction between Cu(II) ions..2. Mononuclear complex [Co(His)2(N₃)]·2H₂O (2) was synthesized by using Histidine and N₃ as as ligands and characterized by IR,elemental analysis and single crystal X-ray diffraction analysis. The results revealed that complex (2) crystallized in the monoclinic space group C2 with a = 25.653(3), b = 8.843(3), c = 8.0767(13) A,β=98.184(2)A. Each Co(Ш) ion is six-coordinated in a distorted octahedral geometry. The N₃^- ion coordinates to Co(Ш) ion in a terminal mode. One of the histidine molecules chelates to the Co(III) ion with one carboxyl O atom and the amino group. The other one chelates to the Co(III) ion using one of the N atoms in imidazole ring and the amino group with the carboxylate group free from coordination. The lattice water molecules forms intermolecular hydrogen bonds with the carboxyl O atoms [O(5)-H(13)···O(3)i,2.816 A ,i: x, y+1]; [O(7)-H(3)···O(2)ii,2.702 A;, z; ii: -x+3/2, y-1/2, -z+1.]. This results in the formation of a supramolecular 2-D network by intermolecular hydrogen bonds.3. Two 3D coordination polymers {[Ni(Glu)(H₂O)]·H₂O}n (3), {[Mn(Glu)(H₂O)]·H₂O}n (4) with chiral helical channels were synthesized from the reaction of glutamic acid with nickel salt or manganese salt, respectively. They were characterized by IR, elemental analysis. The results show that complex (3) crystallized in the orthorhombic space group P2₁2₁2₁ with a = 7.160(2), b = 10.385(3), c = 11.173(3) A and complex (4) crystallized in the orthorhombic space group P2₁2₁2₁ with a = 7.201(2), b = 10.632(3), c = 11.506(4) A. The metal ions in two complexes are six-coordinated in a distorted octahedronal geometry. In both complexs, two carboxylate groups of the glutamic ligand present different coordination modes. One chelates to one metal ion using its two carboxylato O atoms. The other one bridges two metal ions with the amino group coordinating to one the metal ion. This kind of connection leads to the construction of a 3D network with 1D chiral helical channels.4. Tetranuclear complex [Ni4(DPK)4(Ala)2](ClO4)2·2H₂O (DPK = (Py)2C(OH)O-) (5) was obtained from the reaction of alanine, di-2-pyridyl ketone and nickel salt and characterized by IR, elemental analysis and single crystal X-ray diffraction. It was shown that complex (5) crystallized in the triclinic space group PÄ«with a = 11.185(6), b = 11.580(6), c =12.649(6) ?,α= 96.751(7),β=105.681(7),γ= 112.231(7)A. Alanine molecule behaves as a bridging- chelating tridentate ligand with one carboxylato oxygen atom and the amino group coordinating to Ni(II) ion and the remaining carboxylato oxygen atom coordinating to another Ni(II) ion. Eight pyridyl N atoms from four DPK ions are all involved in coordination.5. A three-dimensional coordination polymer [Mn(ABA)(N₃)]n (6) was synthesized by using p-aminobenzoic acid and N₃^-as ligand. The compound was characterized by IR, elemental analysis and single crystal X-ray diffraction analysis. It was shown that complex (6) crystallized in the triclinic space group P2(1)/c with a = 9.211(4), b = 11.186(5), c = 8.034(3) A,β=102.365(5)°. Each Mn(II) ion of (6) is six-coordinated in a distorted octahedron. The Mn(II) ions in (6) are bridged byμ2-carboxylate of p-aminobenzoiate ligands and also by N₃ˉanions in aμ3-η3-N,N,N'-bridging mode, constructing 2-D sheet. The further coordination of the amino groups to the Mn(II) ions from the neighboring sheets leads to the formation of a 3-D network structure. Magnetic investigation on complex (6) shows the existences of antiferromagnetic interaction between Mn(II) ions.